While I was cleaning up the wheels for the trailer I found the split ring to be too wide, about 1 1/2 wider than the other non split ring. So thanks to Rob love I have a safety ring rim to closely match the Rim i think is original.
I went and dug out the "spare" that came with the trailer that was damaged beyond repair, see for yourself i don't know how you could do this.
By the way that's a Dunlap Trak Grip
Maybe they didn't figure out the left hand thread!
Anyways I found some info stamped on the rim, 3 51 K 20X6.0 type-RH-5• Patent applied for etc. The little dot beside the five is a small o signifying degree.

Seems to signify 5 degree rims, Ford, commercial pattern wheels....
I thought that was a British/Canadian thing only on 16 inch rims?
Or are these 51 dated as in the first numbers?